Turbulent Flow over Two-Dimensional Rectangular-Shaped Roughness Elements with Various Spacings

The present study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Experiment was performed using PIV technique in the circulating water channel. Results showed that the flow over roughness elements was characterized by the high shear flow emanating from top of roughness element and the recirculating region formed at the trough of two roughness elements. It was also confirmed that k-type roughness is certainly a more effective means than d-type roughness in thickening the viscous layer. In general, the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface.